pthread_mutex_timedlock(), pthread_mutex_timedlock_monotonic()

Attempt to lock a mutex


#include <pthread.h>
#include <time.h>

int pthread_mutex_timedlock( 
                  pthread_mutex_t * mutex,
                  const struct timespec * abs_timeout );

int pthread_mutex_timedlock_monotonic( 
                  pthread_mutex_t * mutex,
                  const struct timespec * abs_timeout );


The mutex that you want to lock.
A pointer to a timespec structure that specifies the maximum time to wait to lock the mutex, expressed as an absolute time.



Use the -l c option to qcc to link against this library. This library is usually included automatically.


The pthread_mutex_timedlock() function locks the mutex object referenced by mutex. If the mutex is already locked, the calling thread blocks until the mutex becomes available as in the pthread_mutex_lock() function. If the mutex can't be locked without waiting for another thread to unlock the mutex, the wait is terminated when the specified timeout expires.

The pthread_mutex_timedlock_monotonic() function is a QNX Neutrino extension; it's similar to pthread_mutex_timedlock(), but it uses CLOCK_MONOTONIC, so the timeout isn't affected by changes to the system time.

By default, if a thread with a higher priority than the mutex owner attempts to lock a mutex, then the effective priority of the current owner is increased to that of the higher-priority blocked thread waiting for the mutex. The owner returns to its real priority when it unlocks the mutex. For more information, see Mutexes: mutual exclusion locks in the QNX Neutrino Microkernel chapter of the System Architecture guide.

The timeout expires when the absolute time specified by abs_timeout passes, as measured by the clock on which timeouts are based (i.e., when the value of that clock equals or exceeds abs_timeout), or if the absolute time specified by abs_timeout has already been passed at the time of the call.

The timeout is based on the CLOCK_REALTIME clock. The timespec datatype is defined in the <time.h> header.

If the mutex can be locked immediately, the validity of the abs_timeout parameter isn't checked, and the function won't fail with a timeout.

As a consequence of the priority inheritance rules (for mutexes initialized with the PTHREAD_PRIO_INHERIT protocol), if a timed mutex wait is terminated because its timeout expires, the priority of the owner of the mutex is adjusted as necessary to reflect the fact that this thread is no longer among the threads waiting for the mutex.


Zero on success, or an error number to indicate the error.


The mutex couldn't be acquired because the maximum number of recursive locks for the mutex has been exceeded.
The current thread already owns the mutex.
The mutex was created with the protocol attribute having the value PTHREAD_PRIO_PROTECT and the calling thread's priority is higher than the mutex' current priority ceiling; the process or thread would have blocked, and the abs_timeout parameter specified a nanoseconds field value less than zero or greater than or equal to 1000 million; or the value specified by mutex doesn't refer to an initialized mutex object.
The owner of the lock died while holding it.
The mutex couldn't be locked before the specified timeout expired.


pthread_mutex_timedlock() is POSIX 1003.1 THR TMO; pthread_mutex_timedlock_monotonic() is QNX Neutrino

Cancellation point No
Interrupt handler No
Signal handler Yes
Thread Yes

See also:

pthread_mutex_destroy(), pthread_mutex_lock(), pthread_mutex_trylock(), pthread_mutex_unlock(), timespec

Mutexes: mutual exclusion locks in the QNX Neutrino Microkernel chapter of the System Architecture guide